Historical flash floods retromodelling in the Ondara River in Tàrrega (NE Iberian Peninsula)

Abstract

Abstract. Flash floods in the Ondara River have caused many fatalities and damages in the town of Tàrrega in the last 400 yr. Unfortunately, no flow records are available.However, floods can sometimes be reconstructed thanks to available historical information: limnimarks, written accounts and archaeological surveys. Indeed, from these data and using the retromodelling method on three different scenarios to take into account morphology changes, the peak flows of the seven greatest floods occurred in Tàrrega since the 17th century were estimated.The results showed that the heaviest flood's specific peak flow (10.7 m 3 s −1 km −2 ) ranks among the highest ever modelled or measured in similar-sized catchments in the Western Mediterranean region. The results pointed out, as well, that the changes in channel's morphology (mainly, the disappearance of a mediaeval bridge under sediment) caused by one of the floods increased the hydraulic capacity of a crucial crosssection. All this resulted in modest floods invading the town less often, but with much faster and, thus, more destructive flows.A preliminary estimation of the results' uncertainty was 4 % for great floods and 18 % for modest floods.The reconstructed peak flows will be introduced in a database for a future use in climatic and hydrological studies.

The "Prediflood" database of historical floods in Catalonia (NE Iberian Peninsula) AD 1035–2013, and its potential applications in flood analysis

“…These compilations done with scientific purposes, although scarce and modest, follow the methods of European research. This has allowed complex analyses such as: the improvement of climate behaviour estimations from multicentennial flood chronologies Barriendos and Rodrigo, 2006); the study of flash floods (Llasat et al, 2003;Barrera et al, 2006;Balasch et al, 2010aBalasch et al, , 2011; or the reconstruction of the peak flows and the impacts of one of the worst floods in the Iberian Peninsula, that of November 1617 (Thorndycraft et al, 2006).…”

“…Besides, a high standard of accuracy in the calculations is not essential in reconstructing historical flows, because the input data have themselves a high degree of uncertainty. Because of this, and for the sake of homogeneity between data-rich and data-poor sites, we systematically use the 1-D hydraulic model HEC-RAS in steady flow conditions (USACE, 2008), which gives accurate enough results (Balasch et al, 2010a(Balasch et al, , 2011. Nevertheless, we also apply the 2-D model of Iber (Iber 2010;Ruiz-Villanueva et al, 2013) in some cases which would otherwise produce excessive inaccuracy: highly urbanized or very sinuous reaches or with large floodplains.…”

“…Unfortunately, both the frequency and magnitude of floods are likely to increase in the near future due to climate change, thus worsening the effects of floods on the human population. This is especially true for the Mediterranean region, where climatic models foresee an increase of rainfall irregularity: in Catalonia (NE Iberian Peninsula), for the period 2070-2100, models estimate a 15 % decrease in total rain depth but, at the same time, a 15-30 % increase in the number of days with heavy precipitation (Barrera and Cunillera, 2011). In central Europe, torrential precipitation will also increase in the near future, although this cannot be assured to cause an increase in river flows, due to the short length of the data series (IPCC, 2014;Kovats and Valentini, 2014).…”

The "Prediflood" database of historical floods in Catalonia (NE Iberian Peninsula) AD 1035–2013, and its potential applications in flood analysis

“…These compilations done with scientific purposes, although scarce and modest, follow the methods of European research. This has allowed complex analyses such as: the improvement of climate behaviour estimations from multicentennial flood chronologies (Llasat et al, 2005;Barriendos and Rodrigo, 2006); the study of flash floods (Llasat et al, 2003;Barrera et al, 2006;Balasch et al, 2010aBalasch et al, , 2011; or the reconstruction of the peak flows and the impacts of one of the worst floods in the Iberian Peninsula, that of November 1617 (Thorndycraft et al, 2006).…”

Historical, hydraulic, hydrological and meteorological reconstruction of 1874 Santa Tecla flash floods in Catalonia (NE Iberian Peninsula)

“…Luckily, there is a lot of information about this event, especially, maximum water depths in many locations. So far, some of this information has already been used to calculate the peak flows of the floods in six spots located in three catchments (Balasch et al, 2010a(Balasch et al, , 2011. Here, we enlarged this list with four more sites and two more catchments.…”